Process for production of 2-(aminophenyl)-2, 1, 3-benzotriazole



United States Patent 3,153,048 PRGCESS FOR PRODUQTION 0F 2-(0=AMWG- PHENYL)-2,1,3-BENZOTRIAZOLE Donald N. Thatcher, Pitrnan, N.J., assignor to E. 1. du Pont de Nemours and Company, Wilmington, Del, a corporation of Delaware No Drawing. Filed .l'uly 20, 1962, Ser. N 211,385 it) Ciairns. (Ci. 260--308) The present invention relates to an improved process for the preparation of 2-(o-aminophenyl)-2,1,3-benzotriazole, a valuable intermediate for ultraviolet light absorbers, dyes and pigments.

In copending application No. 173,806, filed February 16, 1962, in the name of R. A. Carboni is described the preparation of 2 (o aminophenyl) 2,1,3 benzotriazole from o,o-diaminoazobenzene. At present, 0,0- diaminoazobenzene is prepared in relatively low yields by the oxidation by lead oxide of o-phenylenediamine, a high-priced material of limited availability.

To permit a reduction in the cost of Z-(o-arninophenyl)-2,1,3-benzotriazole, a process has been needed which provides the compound in improved yields from low-cost and readily available starting materials. The present invention provides such a process.

In accordance with the present invention, 2-(o-amino phenyl)-2,l,3-benzotriazole is prepared by a process which comprises (1) contacting, in an aqueous solution of a salt of a weak base and a strong acid, o-nitroacetanilide with finely divided zinc or magnesium to form an o-hydroxylaminoacetanilide solution, (2) mixing said solution of o-hydroxylarninoacetanilide with o-nitrosoacetanilide to form o,o'-diacetamidoazoxybenzene, (3) heating the o,o'-diacetarnidoazoxybenzene with strong sulfur-free mineral acid to form the acid salt of o,o'-diarninoazoxybenzene, (4) contacting the said acid salt with a base to form o,o'-diaminoazoxybenzene, and (5) heating the o.,o-diaminoazoxybenzene in the presence of polyphosphoric acid.

The o-nitrosoacetanilide with which o-hydroxylamino it If-C-OHa N-C-QH; Zn or Mg I NO NHOH aq. NHzGl o-Hydroxylaminoo-Nitroaeetanllide acetanihde l oxidizing agent o-Nitrosoaeetanilide In the reduction of o-nitroacetanilide by finely divided zinc ormagnesium in aqueous ammonium chloride, at

amine. Preferably, between about 3 and 5 molesof fine 1y divided zinc or magnesium, i.e., having a particle size such that the particles pass through a 325-rnesh Tyler screen and are held on a 40-mesh Tyler screen, are used for each mole of o-nitroacetanilide. The use'of metal particles larger or smaller than this size is less economical. Zinc is the preferred finely divided metal.

The above reduction is carried out in the presence of an aqueous buffer solution, preferably an ammonium chloride solution, although other salts of a weak base and a strong acid may be used, e.g., calcium chloride and dimethylammonium chloride. Theminimum amount of ammonium chloride usually used is one-third (molar ratio) the amount of metal present. No maximum limitation exists to the amount of ammonium chloride which can be present except for economics. two runs identical except that the amount of ammonium chloride used in one run was double that used in the other, the conversion to the hydroxylamine was the same.

The choice of zinc dust and ammonium chloride as a reducing agent is dictated by the requirements of the reduction. Under acid conditions, reduction of aromatic nitro compounds generally gives the amino derivative while neutral or basic media favor coupled products if the reducing agent is not too strong. The formation of a phenylhydroxylamine leads to azoxybenzenes by either a coupling reaction with nitrosobenzene or by self oxidation-reduction in basic media to give aniline and azoxybenzene. Thus, neutral media will give the best yields of azoxybenzene if the coupling of 1 mole of phenylhydroxylamine and 1 mole of nitrosobenzene can be carried out; Thus the choice of such reagents as magnesium and ammonium chloride,' zinc and ammonium chloride are preferred over more basic reagents such as zinc and sodium hydroxide or strong base and an alcohol or a sugar.

compounds with ortho-substituents. Also strong bases.

o,0-Diacetamidoazoxybenzene lj hydrolysis 2) neutralization o,o'-Diarninoazoxybenzene 3,153,348 Patented 0st. 13, 1964 For example, in g will cause hydrolysis of the acetamido group in this case, leading to free aromatic amines which are subject to oxidation in basic media.

Although the order of addition of the zinc and ammonium chloride to o-nitroacetanilide is not critical, yields are slightly higher when the zinc is suspended in the solution of o-nitroacetanilide and the ammonium chloride subsequently is added to the suspension. Although water alone is satisfactory as the solvent for the ammonium chloride, the presence of an alkanol in admixture therewith is sometimes advantageous. Preferred alkanols are the 1-3 carbon alkanols. Water should usually comprise at least 20% by weight of the mixture.

The reduction of o-nitroacetanilide can be carried out at a temperature of from 5 to +100 C. At a temperature below 5 C., the reaction rate is so low as to be economically unfeasible. At a temperature above 100 C., the o-nitroacetanilide converts predominantly to the amine. The preferred temperature for the reduction of o-nitroacetanilide is between about 15 and about 50 C.

The time of reaction is not critical. Since the reduction reaction is exothermic, the reaction is considered complete when no further increase in temperature is ob served.

0,0'-Diacetamidoazoxybenzene is formed by the coupling of o-hydroxylaminoacetanilide and o-nitrosoacetanilide. The latter compound may be prepared conveniently by the oxidation of the hydroxylamine. In the process of this invention, the hydroxylamine from the reduction preferably is not isolated as such but is used in the form of a solution. Thus, the coupling can be obtained by mixing a solution of the hydroxylamine with separately prepared o-nitrosoacetanilide or by mixing an oxidizing agent in controlled amounts with the solution of the hydroxylamine to provide in situ prepared o-nitrosoacetanilide from a portion of the hydroxylamine.

The oxidizing agents suitable for preparing the o-nitrosoacetanilide separately or in situ are the conventional oxidizing agents, for example, strong oxidizing agents such as nitric acid and the alkali metal dichromates, permanganates, and hypochlorites and Weaker oxidizing agents, such as ferric chloride-sodium acetate solutions, potassium iodide-iodine solutions, Fehlings solution, and potassium ferricyanide. The solution can be neutral, acidic, or basic, depending upon the choice of oxidizing agent. Inasmuch as the oxidation of a hydroxylamine to the corresponding nitroso compound is conventional in the art, the separate preparation of the o-nitrosoacetanilide is not part of this invention. Further, it is within the scope of this invention to use o-nitrosoacetanilide prepared other than by the oxidation of the corresponding hydroxylamine.

In the case of in situ preparation of the o-nitrosacetanilide by the oxidation of a portion of the o-hydroxylaminoacetanilide, the amount of oxidizer added must be controlled so that preferably up to 50% of the hydroxylamine is converted to o-nitrosoacetanilide. The remaining hydroxylamine is then available for coupling with the o-nitrosoacetanilide formed to prepare o,o-diacetamidoazoxybenzene. The rate for the coupling reaction is much lower than is the rate of the oxidation reaction.

In the absence of air, the amount of oxidizer required would be half the stoichiometric amount required to oxidize all of the hydroxylamine derivative to the nitroso compound. In the presence of air, considerably less oxidizer is required, the air serving to either oxidize a portion of the hydroxylamine or to regenerate the added oxidizer or both. Oxidation by air alone is feasible, however, the rate is undesirably low. Thus, the preferred condition for this step involves the use of an added oxidizer and operation in the presence of air. In general, the amount of oxidizer to be added will be from 25% to 100% of that required to convert one-half of the hydroxylamine to the corresponding nitroso compound when air is present. The mole ratio of oxidizer to hydroxylamine will, of course, depend upon the specific oxidizer used. For example, when ferric chloride-sodium acetate is the oxidizer, the amount of ferric chloride can range from 0.5 to 1.2 mole for each mole of the hydroxylamine. When more than 1.2 mole of ferric chloride is used per mole of hydroxylamine, the major portion of the oxidation product will be the nitroso compound and, of course, insufiicient hydroxylamine remains for coupling with all of the nitroso compound. When less than 0.5 mole of ferric chloride is present for each mole of the hydroxylamine, small yields of the desired o,o-diacetamidoazoxybenzene result because of insuflicient nitroso compound being formed to couple with the hydroxylamine. The preferred amount of ferric chloride used is between 0.8 and 1.2 moles based on one mole of the hydroxylamine. The amount of sodium acetate used in conjunction with the ferric chloride is, of course, dependent on the amount of ferric chloride. The sodium acetate acts as a hydrogen halide acceptor for maintaining the pH of the reaction mixture between 4 and 9. The mole ratio of sodium acetate to ferric chloride is at least one mole per mole of ferric chloride and is preferably from about 3 to 5 moles per mole of ferric chloride.

The temperature of the partial oxidation of the hydroxylamine solution and the coupling of the o-nitroso acetanilide with the hydroxylamine to form o,o'-diacetamidoazoxybenzene generally is carried out between -5 and about C. Below 5 C., the reaction rate is so low as to be economically unfeasible. Above 100 C., the formation of by-products is encouraged. The preferred temperature range is between 1550 C. For practical purposes the oxidation reaction is effected at the same temperature as is the reduction reaction.

The reaction medium in the oxidation of the hydroxylamine and the coupling of the hydroxylamine with the nitroso compound is conveniently that employed in the reduction step.

The 0,0-diacetamidoazoxybenzene is recovered conventionally by precipitation from the reaction mixture, followed by physical separation, e.g., by filtration, centrifuging, etc.

To form the acid salt of o,o-diaminoazoxybenzene, the o,o-diacetamidoazoxybenzene is heated with a strong mineral acid, e.g., concentrated (37%) hydrochloric acid, for example, at a temperature at from about room temperature to the reflux temperature of the acid. Preferably, the react-ion is carried out at the reflux temperature of the mixture, i.e., about 7080 C., usually in an aqueous medium. Dilute hydrochloric acid can be used for the hydrolysis but is not recommended because of the longer heating period required and solubility of the salt. In addition to hydrochloric acid, other strong mineral acids, which can be used include, e.g., phosphoric acid, perchloric acid, etc. Heating of the mixture is discontinued upon precipitation of the acid salt of o,o-diaminoazoxybenzene. The precipitate is separated by conventional methods, e.g., filtered, washed, filtered, and dried.

ethanol is particularly convenient as a wash solution because it precludes a subsequent filtering and drying step, although water can be used, followed by filtration and drying. When phosphoric acid is used as the hydrolyzing agent, the resulting phosphate salt need not be neutralized but can be directly cyclodehydrated.

The acid salt, e.g., hydrochloride, of o,o'-diaminoazoxybenzene can be neutralized by conventional agents, e.g., ammonium hydroxide (preferred) or pyridine or, if caution is exercised, at strong base, e.g., sodium or potassium hydroxide. The resulting solid o,o-diaminoazoxybenzene is recovered conventionally by filtration, centrifuging, etc.

The dehydration-cyclization of the o,o'-diaminoazoxybenzene to a 2-(o-aminophenyl)-2,1,3-benzotriazole is accomplished by the use of polyphosphoric acid. The weight ratio of polyphospheric acid to oo'-diaminoazoxybenzen is normally between about to 1 and 50 to l, and at least /1. The polyphosphoric acid which acts as solvent-reactant is generally heated to a temperature of about 80 C. to adjust the viscosity prior to the addition of 0,0-diaminoazoxybenzene. The resulting mixture is then heated to a temperature up to 200 C. Above 200 C., degradation occurs. The mixture is preferably heated to a temperature between about 100-125 C. Polyphosphoric acid is a commercially available mixture of phosphoric acids (orthophosphoric acid, pyrophosphoric acid and linear polyphosphoric acids) having a theoretical P 0 content of 81-85% (Popp, Frank D. and McEwen, William B, Chemical Reviews 58, pp. 321-323 (1958)).

The isolation of the desired 2-(o-aminophenyl)-2,1,3- benzotriazole is not crtical and can be ellected by adding the cooled reaction mixture to twice its volume of cold water and filtering the solids from the mixture. The Z-(O-aminophenyl)2,l,3-benzotriazole can be extracted from the aqueous filtrate with a suitable solvent, e.g., chloroform, and, after separation of the two layers, the solvent can be removed by conventional methods, e.g., evaporation, to give solid Z-(o-aminophenyl)-2,1,3-benzotriazole. Additional 2-(o-aminophenyl)-2,1,3-benzotriazole can be recovered from the filter cake by neutralizing the salt of 2-(o-aminophenyl)-2,1,3-benzotrlazo1e, for example, with ammonium hydroxide, as shown in Example 4, and recovering the desired product conventionally.

As indicated in the aforementioned application Serial No. 173,806, the Z-(o-aminophenyl)-2,1,3-benzotriazole obtained in accordance with this invention can be readily converted to corresponding N-monoacylamides by conventional techniques, e.g., by reacting the free amine group with an equivalent amount of acylating agent, preferably in the presence of an acid acceptor such as an alkali metal hydroxide or a tertiary amine such as pyridine or triethylamine. Thus, for example, Z-(o-N-monobenzamidophenyl)-2,1,3-benzotriazol can be prepared by the reaction of 2-(o-aminophenyl)-2,l,3-benzotriazole with benzoyl chloride in the presence of aqueous sodium hydroxide, while 2-(o-N-monostearamindophenyl)-2,l,3- benzotriazole can be prepared by a similar reaction in tetrahydrofuran of stearoyl chloride with 2-(o-aminophenyi)-2,l,3-benzotriazole in the presence of triethylamine. The 2-(o-aminophenyl)-2,1,3-benzotriazole, and particularly the amide derivatives thereof such as those just mentioned, find sorbers in the photostabilization of both natural and synthetic polymers. Usually, about from 0.01 to about 5% by weight of photostabilizer based on the weight of polymer is employed. Thus, for example, the 2-(o-aminophenyl)-2,1,3-benzotriazole or the amide derivatives thereof can be incorporated into such polymers as polyethylene, polystyrene, polyvinyl chloride or ethyl cellulose by solution blending or milling techniques and cast, pressed, rolled or otherwise formed into films and coatings with outstanding light stability. Srnall proportions of the 2-(0- aminophenyl)-2,1,3-benzotriazole also can be copolymerized with, for example, diamines and dibasic acids in the preparation of polyamides to yield polymers of improved light stability. In addition, the Z-(o-aminophenyl)-2,1,3-benzotriazole can be diazotized to form dyestutfs and pigments.

The following examples illustrate the process of the invention. The parts and percentages in the examples are parts by weight. The poly phosphoric acid used in the cyclodehydration step had a phosphoric anhydride (P 0 content of 82-84%.

Pre oration o 0,0'-Diacetamid0azoxybenzene Example 1.To an aqueous slurry of 10 parts (0.06)

wide utility as ultraviolet light ab-" mole of o-nitroacetanilide and 8.2 parts (0.15 mole) of ammonium chloride in 140 parts of water at 0 C. was added 16 parts (0.25 mole) of finely divided zinc. After the slurry had changed color from yellow to white, the Zinc compounds were filtered from the reaction mixture and the filtrate passed directly into a solution of 8.8 parts (0.05 mole) of o-nitrosoacetanilide in 405 parts of methanol. During this addition, the solution immediately changed from green solution of o-nitrosoacetanilide to yellow and o,o-diacetamidoazoxybenzene began to precipitate. The methanol solution was reduced to approximately one-half volume by evaporation, cooled, and filtered. o,o'-diacetarnidoazoxybenzene (14.7 parts), Ml. 179-182 C. was obtained. Water was added to the filtrate and additional material precipitated. The additionel amountof o,o' diacetamidoazoxybenzene obtained was 0.7 part, MP. 178-181 C. The total yield of 0,0'-diacetamidoazoxybenzene, based on o-nitroacetanilide in this step, Was approximately 92%. i

The following example illustrates the preparation of 0,0-diacetarnidoazoxybenzene by partial oxidation of the solution of the hydroxylamine.

Example 2.--To a slurry of parts (0.14 mole) of o-nitroacetanilide and parts (0.61 mole) of zinc dust in 350 parts of water at room temperature was added 13 parts (0.24 mole) of solid ammonium chloride. After the slurry had changed color from yellow to white, the zinc compounds were removed from the slurry, by filtration. To the filtrate was added dropwise a solution of 19 parts (0.07 mole) of ferric chloride hexahydrate and 3.83 parts (0.05 mole) of anhydrous sodium acetate in 30 parts of water. Themixture was stirred for /2 hour.

A yellow solid precipitated and was filtered from the mixture. This solid (12.7 parts, 57% yield) was identifield as o,o'-diacetarnidoazoxybenzene, MP. 177-182 C.

Preparation of o,o'- Diaminoazoxybenzene product was obtained from the alcohol wash. Infrared chloride dissolved centrated to /3 volume and cooled.

analysis indicated this product to be the desired hydrochloride, 97.8% yield. To a suspension of 3 parts of the hydrochloride in 40 parts of methanol was added 6.6 parts of 28% ammonium hydroxide. All of the hydroand the methanol solution was con- The solid material which precipitated was removed by filtration and dried to give 2.3 parts of o,o-diaminoazoxybenzene.

Preparation of 2-(o-Amin0phenyl)-2,1,3-Benz0triaz0le Example 4.-o,o-Diaminoazoylbenzene (5 parts) was dehydrated-cyclized by adding 150 parts of polyphosphoric acid heated to C. and heating the mixture to -116. C. for 1 hour with stirring. After this period, the mixture was allowed to cool and was then poured, with agitation, into twice its volume of water. After the mixture was stirred for 20 minutes, the solids were filtered from the mixture and dried to give 3.7 parts of material having a M.P. of approximately C. The aqueous filtrate then was extracted twice with chloroform and the two layers were separated. The chloroform was evaporated from the extract layer to give 2.5 parts of a solid having a M.P. of 91-93 C. This solid was identified by infared spectra and mixed 2,1,3-benzotriazole. The above solid material melting at approximately 195 C. obtained in the aqueous filtration The suspension was cooled and filtered melting point as 2-(o-aminophenyl)- was identified by its infrared spectrum as a salt of 2-(0- aminophenyl) 2,1,3 benzotriazole. This material was suspended in 40 parts of methanol and the suspension was made basic with ammonium hydroxide. The methanol was evaporated and the resulting solid was recrystallized from cyclohexane to give 0.75 part of Z-(o-aminophenyD- 2,1,3-benzotriazole. The total conversion to 2 (o aminophenyl)-2,1,3-benzotriazole was 70.4% and the yield was 79.5%.

Example 5.Following the procedure of Example 2 except substituting magnesium for the zinc, the yield and conversion of the desired product are essentially the same.

I claim:

1. A process for the preparation of 2-(o-aminophenyl)- 2,1,3-benzotriazole which comprises:

(a) contacting, in an aqueous solution of a salt of the group consisting of ammonium chloride, calcium chloride, and dimethylammonium chloride, o-nitroacetanilide with a finely divided metal selected from the group consisting of zinc and magnesium to form an o-hydroxylaminoacetanilide solution,

(b) mixing said aqueous solution of o-hydroxylaminoacetanilide with o-nitrosoacetanilide to form o,o,'-diacetamidoazoxybenzene,

(c) heating said o,o-diacetamidoazoxybenzene with strong sulfur-free mineral acid to form the acid salt of o,o-diaminoazoxybenzene,

(d) contacting said acid salt with base to form o,o'-

diaminoazoxybenzene, and

(e) heating said o,o'-diaminoazoylbenzene in the pre ence of polyphosphoric acid.

2. A process of claim 1 wherein said metal is present in an amount of at least 2 moles per mole of o-nitroacetanilide.

3. A process of claim 2 wherein the mole ratio of said salt to said metal is at least 4. A process for the preparation of 2-(o-aminophenyl)- 2,1,3-benzotriazole which comprises:

(a) contacting, in aqueous ammonium chloride, o-nitroacetanilide with finely divided zinc to form an o-hydroxylaminoacetanilide solution,

(b) mixing said solution with an oxidizing agent in an amount sufficient to convert part of the o-hydroxylaminoacetanilide to o-nitrosoacetanilide whereby said o-nitrosoacetanilide reacts with the remaining o-hydroxylaminoacetanilide to form o,o'-diacetamidoazoxybenzene,

(c) heating said o,o-diacetamidoazoxybenzene with strong sulfur-free mineral acid to form the acid salt of 0,0'-diaminoazoxybenzene,

(d) contacting said acid salt with base to form 0,0-

diaminoazoxybenzene, and

(e) heating said o,o'-diaminoazoxybenzene in the presence of polyphosphoric acid.

5. A process for the preparation of 2-(o-aminophenyl)- 2,1,3-benzotriazole which comprises:

(a) contacting, in aqueous ammonium chloride, o-nitroacetanilide with about from 3 to 5 moles of finely divided zinc per mole of o-nitroacetanilide to form an o-hydroxylaminoacetanilide solution, the mole ratio of ammonium chloride to zinc employed being at at least about A,

(b) mixing at a temperature of about from -5 to +100 C. said aqueous solution of o-hydroxylaminoacetanilide with o-nitrosoacetanilide to form 0,0- diacetamidoazoxybenzene,

(c) heating said o,o-diacetarnidoazoxybenzene with concentrated hydrochloric acid to form the hydrochloride salt of o,o'-diaminoazoxybenzene,

(d) contacting said hydrochloride salt with aqueous ammonium hydroxide to form o,o'-diaminoazoxybenzene, and

(e) heating said o,o-diaminoazoxybenzene in the presence of polyphosphoric acid at a temperature of about from to 200 C.

6. A process of claim 5 wherein said o-nitrosoacetanilide is prepared in situ by the oxidation, at a pH of about from 4 to 9, of part of said o-hydroxylaminoacetanilide with aqueous ferric chloride in the presence of sodium acetate.

7. A process for the preparation of 2-(o-aminophenyl)- 2,1,3-benzotriazole which comprises:

(a) contacting, in aqueous ammonium chloride, o-nitrosoacetanilide with at least 2 moles of Zinc per mole of o-nitrosoacetanilide in form an o-hydroxylaminoacetanilide solution, the mole ratio of ammonium chloride to zinc employed being at least about /a,

(b) mixing at a temperature of about from -5 to C. said aqueous solution of o-hydroxylaminoacetanilide with o-nitrosoacetanilide to form o,o'-diacetamidoazoxybenzene,

(c) heating said o,o-diacetamidoazoxybenzene with phosphoric acid to form the phosphate salt of 0,0- diaminoazoxybenzene, and

(d) heating said salt in the presence of polyphosphoric acid at a temperature of about from 80 to 200 C.

8. A process as claimed in claim 1 wherein said metal is zinc.

9. A process as claimed in claim 1 wherein said metal is magnesium.

10. A process as claimed in claim 1 wherein said salt of a weak base and a strong acide is ammonium chloride.

References Cited in the file of this patent UNITED STATES PATENTS 2,458,214 Souders Jan. 4, 1949 2,985,661 Hein et a1 May 23, 1961 OTHER REFERENCES Cusmano: Chem. Abstracts, vol. 15, pages 28401 (1921).

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pa tent N0 3 153 048 October 13 1964 Donald N, Thatcher It is hereby certified that error appears in the above numbered .patent requiring correction and that the said Letters Patent should read as corrected below Column 7, line 31 for "-diaminoazoylbenzene" read d1am1noezoxybenzene column 8 line 29, for "in" read to l1ne 416 for "acide" read acid Signed and sealed this 9th day of March 1965.

(SEAL) I;

Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent. No. 3, 153 048 7 October 13 1964 Donald N. Thatcher It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below,

Column '7 line 31, for "diaminoazoy1benzene" read diaminoazoxybenzene column 8 line 29 for "in" read to line 46, for "acide" read acid Signed and sealed this 9th day of March 1965.

. Attest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A PROCESS FOR THE PREPARATION OF 2-(O-AMINOPHENYL)2,1,3-BENZOTRIAZOLE WHICH COMPRISES: (A) CONTACTING, IN AN AQUEOUS SOLUTION OF A SALT OF THE GROUP CONSISTING OF AMMONIUM CHLORIDE, CALCIUM CHLORIDE, AND DIMETHYLAMMONIUM CHLORIDE, O-NITROACETANILIDE WITH A FINELY DIVIDED METAL SELECTED FROM THE GROUP CONSISTING OF ZINC AND MAGNESIUM TO FORM AN O-HYDROXYLAMINOACETANILIDE SOLUTION, (B) MIXING SAID AQUEOUS SOLUTION OF /-HYDROXYLAMINOACETANILIDE WITH O-NITORSOACETANILIDE TO FORM O,O'',-DIACETAMIDOAZOXYBENZENE, (C) HEATING SAID O,O''-DIACETAMIDOAZOXYBNEZENE WITH STRONG SULFUR-FREE MINERAL ACID TO FORM THE ACID SALT OF O,O''-IDAMINOAZOXYBENZENE, (D) CONTACTING SAID ACID SALT WITH BASE TO FORM O,O'' DIAMINOAZOXYBENZENE, AND (E) HEATING SAID O,O''-DIAMINOAZOYLBENZENE IN THE PRESENCE OF POLYPHOSPHORIC ACID. 